Modern residential, commercial, and industrial buildings generally include systems for exchanging air between the inside and outside of the building, as well as between different sections of the building. In that regard, virtually all air exchanger systems provide fresh or recirculated air to the building. The volume and source of the exchanged air can be controlled to achieve the desired ventilation.
An air exchange system may also be designed to control the ingress and egress of gases, vapors, and particulate with respect to a ventilated space. For example, by introducing more air than it draws from a room, an air exchange system increases the pressure of the air in the room above that of the surrounding atmosphere. As a result, air will flow out of the room through any openings that might otherwise allow undesired gases and particulate to enter. By withdrawing more air from the room than is introduced, the air exchange system has the opposite effect.
Most air exchange systems also include some provision for controlling the temperature of the exchanged air. The desired temperature of the area being serviced is usually a function of the manner in which the area is used. To achieve the desired temperature, the exchange system may need to heat or cool the air supplied to the area, depending upon the initial temperature of the area and the source of the air used.
Conventional heating, ventilation, and cooling (HVAC) air exchange systems employ separate, and often independent, components or subsystems to achieve these functions. Addressing each of these components in greater detail, a basic ventilation system will be considered first. Such a ventilation system includes a blower, control circuit, filter, and housing.
The blower is regulated by the control circuit and is responsible for establishing airflow between the system and the ventilated room. In that regard, an air inlet and air outlet are provided between the ventilation system and the ventilated room. The blower may be located at the air inlet to force air into the room, with air escaping from the room through the air outlet. Alternatively, the blower may be located at the air outlet to draw air out of the room, with fresh air entering the room through the air inlet.
A somewhat more complex ventilation system includes two blowers. Specifically, a supply blower is provided adjacent the air inlet and a return blower is located adjacent the air outlet. With two blowers employed, the load on each blower is less than would be experienced by a single blower. In addition, the use of separate inlet and outlet blowers allows the control circuit to easily regulate the relative rates of air supply and return to achieve underpressure or over-pressure ventilation.
Turning now to a discussion of the heating systems employed in air exchange systems, such systems commonly employ a heat source, heat transfer system, blower, and control circuit. The heat source converts energy from, for example, gas or electricity into thermal energy. The transfer system usually forms a closed loop that couples the heat source and the airflow path.
In that regard, the transfer system may include a transfer coil, positioned in the airflow path and coupled to the heat source by a pair of conduits. A pump circulates fluid heated by the heat source to the coil, where the fluid's heat is transferred to the air. The coil preferably has a relatively large surface area, allowing it to efficiently transfer heat from the fluid to the air.
The heating system blower is responsible for circulating air between the room to be heated and the transfer coil. In that regard, the blower draws air from the room through an air inlet and forces it across the transfer coil. The heated air is then returned to the room through an air outlet.
The control circuit of the heating system allows the temperature of the air in the room to be regulated. The control circuit typically includes an input control that generates an input signal indicative of a desired room temperature selected by an operator. A temperature sensor similarly generates an input signal indicative of the room's actual temperature. The control circuit regulates the operation of the heat source and blower, based upon the feedback obtained from the input signals, to produce the desired room temperature.
Some heating systems exhaust air to the environment, rather than recirculating it to the room being heated. In such systems, an effort is often made to recover heat from the air before it is exhausted. Heat recovery usually involves the addition of a second heat transfer coil to the closed loop of the heating system. The second coil is coupled between the first coil and the heat source and is positioned in the path of the air being drawn from the room. As a result, the air's thermal energy is transferred to the second coil rather than to the environment. Fluid circulation between the second coil and first coil then allows this energy to be transferred to the air entering the room, avoiding energy loss that would otherwise occur.
The third component of an air exchange system to be discussed is the cooling system. In that regard, a conventional cooling system typically includes an evaporator, compressor, condenser, expansion valve, supply blower, exhaust blower, and control circuit.
Reviewing the operation of these elements, the evaporator is a coiled tube containing a refrigerant at a relatively low pressure. As the pressure of the refrigerant is lowered, the refrigerant evaporates, cooling the evaporator. The compressor then pumps the vaporized refrigerant from the evaporator to the condenser.
At the condenser, which is also a coiled tube, the pressure of the refrigerant is increased. When a sufficiently high pressure is reached, the refrigerant condenses back into liquid form, transferring heat to the condenser. The liquid refrigerant Is then returned to the evaporator through the expansion valve at the desired low pressure.
This evaporation/condensation cycle is used to cool the air supplied to the room in the following manner. The evaporator is positioned in the airflow path, for example, adjacent the air supply outlet. The supply blower draws air from the room through an air inlet and forces it over the evaporator's coils before returning it to the room through a supply outlet. As a result, the air supplied to the room is cooled.
The condenser, on the other hand, is not positioned in the path of the air supplied to the room. Rather, the condenser is located adjacent an air exhaust outlet, which opens to the outside environment. Air is drawn from the air inlet by the exhaust blower and forced across the condenser to remove heat from the condenser. The warm air is then passed to the environment through the exhaust outlet.
Like the control circuit of a heating system, the cooling system control circuit allows the temperature of the air in the room to be regulated. The control circuit typically includes an input control that generates an input signal indicative of a desired room temperature selected by an operator. A temperature sensor similarly generates an input signal indicative of the room's actual temperature. The control circuit regulates the operation of the evaporation/condensation cycle and the blowers, based upon feedback obtained from the input signals, to produce the desired room temperature.
As noted previously, the separate ventilation, heating, and cooling components of an air exchange system are often independently controlled to achieve the desired air circulation and temperature. More sophisticated exchange systems have been developed, however, employing a common control circuit to interactively regulate the operation of the otherwise physically independent components and achieve the desired ventilation and room temperature more efficiently.
For example, an integrated control circuit may include a master operator control that generates an input signal representative of the desired ventilation and temperature to be maintained in a room. A set of sensors may also be included to produce signals indicative of, for example, the actual room temperature and the ambient temperature of the external environment. The control circuit responds to these input signals by cooperatively regulating the operation of the ventilation, heating, and cooling systems to achieve the desired ventilation and room temperature. For example, depending upon the relationship between the room temperature and ambient temperature, the control circuit may be able to raise or lower the room's temperature to a desired level using ventilation alone.
As noted previously, although the air exchange systems discussed above perform heating, ventilation, and cooling, they typically employ discrete subsystems that are independently designed, installed, and maintained. At best, these subsystems are commonly controlled or integrate the functions of heating and ventilation or cooling and ventilation. As a result, conventional HVAC air exchange systems tend to be conglomerations of components that are expensive, complex, and difficult to service and adapt.
Another shortcoming of existing air exchange systems relates to their use in providing heat, ventilation, and air conditioning to a number of areas. In that regard, the problem of multiple-site service is commonly addressed by providing a separate air exchange system for each of the areas to be covered. As will be appreciated, while this technique allows the heating, ventilation, and cooling of each area to be independently controlled, the installation of separate systems can be complicated, time consuming, and quite expensive.
An alternative solution to this multiple-site problem involves the use of a conventional single-site air exchange system, provided with separate ducts to and from each of the areas to be serviced. This approach is less cumbersome and expensive than the redundant system configuration described above. However, a conventional single-site air exchanger offers limited control over the service supplied to the different areas and often lacks sufficient capacity to adequately handle the collective needs of the various sites.
In view of these observations, it would be desirable to provide an air exchanger that efficiently performs heating, ventilation, and cooling in a single, easily installed, serviced, and maintained unit. In addition, it would be desirable to provide a unit that can be quickly, easily, and efficiently modified for use in satisfying the heating, ventilation, and cooling needs of a number of different sites.